A Hybrid Compensation Scheme for the Input Rate-Dependent Hysteresis of the Piezoelectric Ceramic Actuators

A hybrid compensation scheme for piezoelectric ceramic actuators(PEAs)is proposed.In the hybrid compensation scheme,the input rate-dependent hysteresis characteristics of the PEAs are compensated.The feedforward controller is a novel input rate-dependent neural network hysteresis inverse model,while the feedback controller is a proportion integration differentiation(PID)controller.In the proposed inverse model,an input ratedependent auxiliary inverse operator(RAIO)and output of the hysteresis construct the expanded input space(EIS)of the inverse model which transforms the hysteresis inverse with multi-valued mapping into single-valued mapping,and the wiping-out,rate-dependent and continuous properties of the RAIO are analyzed in theories.Based on the EIS method,a hysteresis neural network inverse model,namely the dynamic back propagation neural network(DBPNN)model,is established.Moreover,a hybrid compensation scheme for the PEAs is designed to compensate for the hysteresis.Finally,the proposed method,the conventional PID controller and the hybrid controller with the modified input rate-dependent Prandtl-Ishlinskii(MRPI)model are all applied in the experimental platform.Experimental results show that the proposed method has obvious superiorities in the performance of the system.

Preload characteristics identification of the piezoelectric- actuated 1-DOF compliant nanopositioning platform

Packaged piezoelectric ceramic actuators （PPCAs） and compliant mechanisms are attractive for nanopositioning and nanomanipulation due to their ultra- high precision. The way to create and keep a proper and steady connection between both ends of the PPCA and the compliant mechanism is an essential step to achieve such a high accuracy. The connection status affects the initial position of the terminal moving plate, the positioning accuracy and the dynamic performance of the nanoposi- tioning platform, especially during a long-time or high- frequency positioning procedure. This paper presents a novel external preload mechanism and tests it in a 1-degree of freedom （I-DOF） compliant nanopositioning platform. The 1-DOF platform utilizes a parallelogram guiding mechanism and a parallelogram load mechanism to provide a more accurate actual input displacement and output displacement. The proposed stiffness model simulation results verify the and dynamic model of the platform. The values of the preload displacement, actual input displacement and output displacement can be measured by three capacitive sensors during the whole positioning procedure. The test results show the preload characteristics vary with different types or control modes of the PPCA. Some fitting formulas are derived to describe the preload displacement, actual input displacement and output displacement using the nominal elongation signal of the PPCA. With the identification of the preload characteristics, the actual and comprehensive output characteristics of the PPCA can be obtained by the strain gauge sensor （SGS） embedded in the PPCA.

Design and analysis of an untethered micro flapping robot which can glide on the water

Flapping-wing flying insects possess various advantages,such as high agility and efficiency.The design and manufacture of insect-scale flapping-wing micro aerial vehicle(FWMAV)have attracted increasing attention in recent decades.Due to the limitations of size and weight,the FWMAV with an onboard battery which can fully mimic insect flight has not been achieved.In this work,we design and fabricate a highly integrated flapping-wing microrobot named Robomoth.The Robomoth consists of a carbon chassis,customized power and control devices,and two piezoelectric ceramic actuators symmetrically distributed in the thorax and controlled individually.It weighs 2.487 g,spans 5.9 cm in length,possesses 9 cm of wingspan,and carries a 0.355 g rechargeable lithium battery.We demonstrate the mobility of the Robomoth through untethered gliding and making turns on the water surface.A simplified dynamic model of the flapping system is proposed to explain the relationship between the driving frequency and the flapping amplitude.The Robomoth is one new untethered bioinspired flapping-wing robot that can perform stable water surface motion,which holds potential applications such as search and rescue on the water.The robot can also provide insight for designing insect-scale flying vehicles.